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Quantifying the effectiveness of riparian buffers in three lowland, rural watersheds in the Lower Fraser Valley, British Columbia Elliott, Lea Christine

Abstract

The importance of riparian buffers in protecting water quality and fish habitat in agricultural areas is well documented. However, given the limited availability of financial resources for environmental protection, restoration and management it is necessary for communities to set priorities. The objective of this study was to develop a set of easily measured land-based indicators that effect water quality and aquatic habitat. These indicators were used to develop a riparian buffer assessment that could be used to set protection, restoration and nutrient management priorities. A wide range of land-based indicators that are relatively easy to determine from aerial photographs, Geographic Information System (GIS) measurements, and minimal field work were selected. Their impact on water quality and aquatic habitat was examined. These indicators were measured at two scales: a 200m reach and the entire riparian corridor upstream of each sampling site. The indicators were compared with water quality and aquatic habitat measures to assess their ability to predict in-stream conditions in three watersheds in the Lower Fraser Valley, B.C. Six key indicators that had statistically significant relationships with the instream parameters were found to be the best predictors of the effectiveness of the riparian buffer. These indicators were percent forest in the reach, forest cover conditions in the headwaters, percent channelization, the number of barns/km, percent forest in the riparian corridor and percent agriculture in the riparian corridor. Land indicator conditions of the reach were found to be better predictors of in-stream physical habitat, whereas land indicator conditions of the riparian corridor were found to be better predictors of water quality. The indicators chosen were good predictors of water quality and in-stream physical habitat. At greater than 60% channelization dissolved oxygen concentrations were typically below the provincial guidelines set for salmonid egg and alevin lifestages. Forest cover in the headwaters was more important than forest cover at the site for moderating water temperatures. At greater than 0.6 barns/km significantly higher amounts of in-stream ammonia were recorded suggesting improved manure management is required. A notable increase in the amount of large woody debris and habitat complexity was recorded at greater than 60% forest cover at the reach. Based on the observed relationships and thresholds an easy to use assessment procedure for stakeholders to set restoration and protection priorities for riparian buffers was developed. This evaluation was applied to the three watersheds used in this study and the geographic information system (GIS) based display can now be used by decision makers to set priorities for protection, restoration and nutrient management in the riparian buffer.

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